Is there evidence that shows a threshold of exposure below which radon levels are harmless?

The assertion that there is no established threshold of exposure below which radon is considered harmless is supported by extensive research in the field of radon exposure and its health risks. Numerous studies indicate that radon is a known carcinogen and that even low levels of radon exposure can pose health risks, particularly regarding lung cancer. The consensus among health organizations, including the Environmental Protection Agency (EPA) and the World Health Organization (WHO), is that there is no safe level of radon, as any exposure increases the risk of developing lung cancer. Consequently, the idea that a threshold exists below which radon levels are harmless is not scientifically substantiated, making the claim that there is no safe exposure level accurate.